In the above image, the star PSR J0002+6216 seems to be speeding away from the remnant nebulosity of its supernova and a similar behaviour has been observed for other such stars suggesting they acquired this velocity during or after the supernova. This phenomenon of speeding neutron stars i.e. they having speeds much greater than their progenitor stars is supposed to be due to kicks they acquire during the supernovae. This in itself is an interesting problem.

The kick acquired during a supernova can be due to an asymmetry in the event. During a supernova, the star’s outer layer bounces off the interior, resulting in this dense core called a neutron star. If there is mechanical or convection-related instability inside the star before the supernova this can affect the energetic events inside the star during the process of a supernova. This can push the remnant core (which are neutron stars) in a particular direction. This can result in imparting the velocities at which we see them moving.

One solution to the problem goes to the very fundamental properties observed in our Universe and it comes from Neutrinos. Neutrinos are particles that constitute matter just like electrons and protons do. Particles have handedness (simply right-handed and left-handed) which is related to the direction of their spin axis. All these matter particles have both right-handed and left-handed versions of their matter particle and antimatter particle. But experimentally we have only observed left-handed neutrinos and right-handed antineutrinos (refer h). The other counterparts are thought to be interacting only gravitationally and are also supposed to be massive. These are called sterile neutrinos. During supernovae both neutrinos and sterile neutrinos are produced but due to this asymmetry in their properties and choice of interaction, they can impart kicks to the Pulsars.

One more suggestion exploiting this asymmetry has to do with neutrinos in strong magnetic fields. In strong magnetic fields, the direction in which the neutrino is scattered off the nucleus is biased in some direction (refer i). This on average can lead to neutrino drift to be aligned in some way and lead to asymmetry in supernova.

Another solution is that the kick is post-natal or after the supernova phenomena. There is an asymmetry in the emission of radiation and it is the radiation pressure that accelerates the Pulsar. This can be verified based on velocity and correlation of its spin-down rate as it is the rotational energy that feeds the acceleration engine. Also, the correlation of spin and/or magnetic moment can give insight.

Bow Shocks

Like a boat producing waves on a still water surface or a jet speeding at supersonic speed, the fastly moving Astronomical objects produce bow shocks as they pass through the surrounding medium. The nature of the bow shock depends on the relative velocity of the object and the medium. In the case of B22 the bow shock is produced due to the interaction of its relativistic Pulsar winds and surrounding interstellar medium. The winds bump at high velocity in the ISM. The magnetic fields are also involved in characterising the Bow shocks for these objects.

Bow shocks are common phenomena observed around different types of objects “with magnetic fields or high relative velocity in the medium.” For example, the interaction of Earth’s magnetic field and surrounding plasma also creates some type of bow shock which is due to the slowing down of the plasma as it approaches the Earth’s magnetosphere.

These are some eye candies showing Bowshock formation in different scenarios.